Pydebeziumai : update quickstart credentials, and add troubleshooting guide

### Description
This issue enhances documentation transparency and developer experience in `pydebeziumai`. It qualifies README latency marketing claims to reflect real-world push-based WAL performance, synchronizes quickstart credentials across examples, adds multi-platform setup documentation, and introduces a dedicated troubleshooting guide.

### Goals
1. **Realistic Performance & Latency Documentation**:
- Update `README.md` to accurately describe push-based WAL capture and total vector indexing wall-clock performance (~280–500ms).
- Document `offset.flush.interval.ms` event checkpoint replay behavior on application restart.
2. **Quickstart & Credential Synchronization**:
- Synchronize quickstart password defaults (`"postgrespassword"`) across `README.md` and `examples/`.
- Standardize command examples to cross-platform `python` instead of `python3`.
- Add multi-platform `JAVA_HOME` configuration examples for Linux, macOS, and Windows.
3. **Troubleshooting & FAQ Documentation**:
- Create `docs/troubleshooting.rst` covering port conflicts (e.g. local native Postgres intercepting Docker port 5432), credentials, JVM/JAR setup, and replication slot desyncs.